1. Field of the Invention
In many oil wells, the produced fluid cannot flow to the surface naturally. Accordingly, the well must be equipped with some sort of apparatus located downhole to lift the fluids to the surface. There are several different types of artificial lift systems well known to those skilled in the art. All types of lift apparatus are required to be relatively small diametrically, as most oil wells are fitted with cylindrical casing inside the borehole that is typically 5″ to 8″ in internal diameter, although it may be greater in some cases.
Many oil wells, due to either great depth or high fluid rate potential, or both, require pumping apparatuses that can deliver substantial power to provide the pressure and flow rate needed to lift the produced fluid to the surface. It is the nature of mechanical devices that high power capacity requires increased size, and high power pumping apparatuses are no different, and are typically sized to use as much of the diametric extent of the well casing as possible.
An example of an oil well pumping apparatus adapted for, but limited by, the small diameter of oil well casing is the electric submersible pump, or ESP. A typical ESP installation consists of a multi-stage centrifugal pump driven by a downhole electric motor. Both the pump and motor are attached to a string of tubing that extends from the pump motor assembly downhole to the surface. The motor is supplied electricity via a cable strapped to the outside of the tubing extending from the surface to the motor downhole. The fluid extracted from the geologic formation is increased in pressure by the multi-stage pump to a level that will allow it to flow through the tubing to the surface.
The most obvious configuration of such a pumping apparatus would be to locate the electric motor at the end of the tubing, with the electric cable running directly into the motor. The multi-stage pump would be attached to, and situated below, the motor so that the pump inlet, at the bottom of the pump, would be as low in the well as possible. The problem with this configuration is routing the high-pressure fluid from the pump outlet into the tubing for its passage to the surface. The electric motor is frequently required to be of high power and, hence, large in diameter, and fills most of the available casing internal diameter, leaving no room for the fluid to pass. The only option in such a case, and there are ESPs configured this way, is to use a small diameter motor to allow the fluid to flow around the outside of the motor. The problem with this configuration is not only the low power available with small diameter motors, but with the routing of the high pressure produced fluid into the tubing, which requires packers and seals which are expensive and troublesome. An alternative would be to shroud a small diameter motor with a pressure housing connected to the pump outlet and to the tubing that would allow the high-pressure fluid from the pump to flow past the motor and into the tubing. This configuration has the similar disadvantage of requiring the use of a smaller diameter and, hence, less powerful motor to fit within the pressure housing, which must itself fit inside the well casing.
ESPs get around this problem by placing the motor at the very bottom of the assembly, with the pump above, attached to the tubing. The pump inlet is at the bottom of the pump, but above the motor, and the pump outlet is attached to the tubing such that the high pressure pumped fluid flows into the tubing and up to the surface. There are several disadvantages in locating the pump above the motor, but the flow routing convenience outweighs the several disadvantages.
Another type of oil well pumping apparatus adapted to the diminutive confines of typical oil well casing is the geared centrifugal pump, or GCP, as described in U.S. Pat. No. 5,573,063. The GCP uses a multi-stage centrifugal pump similar to that used in an ESP, but instead of being driven by a downhole electric motor, the GCP pump is driven by a rotating rod drive string extending from a prime mover at the surface, to the multi-stage centrifugal pump downhole, with an intermediate speed increasing transmission interposed along the drive string immediately above the pump, which increases the drive string rotational speed, typically less than 1,000 RPM, to the 3,000+RPM speed required by the centrifugal pump (FIG. 1).
Like the ESP, the GCP components are relatively large in diameter to provide the required power and fill most of the available casing internal diameter, leaving, as with ESPs, inadequate annular space for the pumped fluid to flow to the surface. Unlike an ESP, the pump cannot be directly connected to the tubing with the driving transmission, as the rotating rod drive string is directly connected to the transmission and would have to pass through the multi-stage centrifugal pump. How the routing of the high-pressure fluid is accomplished in the GCP forms the basis of this invention.
2. Overview of the Prior Art
The general type of down hole pumping configuration is now well understood by those skilled in the art. The inventor, a well known expert in the oil patch, has created several innovations related to oil well drilling and production, not the least of which is showcased in his U.S. Pat. No. 5,573,063 for a deep well pumping apparatus. That system is one of several that are ideally suited for adaptation to the present invention.
The inventor is not aware of any system which routes produced fluid as described in this patent description, and a search of the patent art disclosed none. Thomas et al. U.S. Pat. No. 6,645,010 does disclose the placement of multiple conduits of various configurations within a well casing, but in no sense considers, nor inadvertently resolves, the optimum exploitation of available space for delivery of product, addressed by the present invention.